Optical items such as sunglasses, goggles, and corrective lenses and the like with polarizers are preferably used for the purpose of alleviating the glare provided by light reflected by a water surface, a snow surface, a road surface or the like and making outdoor scenes easier to see. When natural light is incident on, and reflected by, a water surface or the like, there is a polarization component which is monotonously increased with respect to the angle of reflection. The above-mentioned optical items utilize a phenomenon that when a polarizer is used such that an absorption axis thereof is horizontal, such a polarization component can be cut. Light can be described and behave by two straight polarizations perpendicular to each other. Therefore, where a vibration component of light which is in a plane including the incident light and the normal direction thereto is p polarization, and a component vibrating in a plane perpendicular to the above-mentioned plane is s polarization, the p polarization of light reflected by a water surface or the like has a minimum point which becomes almost zero at an angle of reflection of 55° or in the vicinity thereof, whereas the s polarization of such light monotonously increases. This s polarization is cut.
There are also transparent optical items such as sunglasses, goggles, corrective lenses and the like including a layer containing a photochromic colorant and thus having photochromic performance of being colored under external light containing a large amount of ultraviolet rays and of being colorless under artificial light containing a small amount of ultraviolet rays.
A known polarizer usable for these items is formed of a resin film, typically, a poly(vinyl alcohol) (PVA) film. Such a film is stretched in one direction while being dyed with iodine or a dichroic dye and thus is provided with polarization properties.
Known methods for providing such a film with photochromic performance include (1) a method of using a polymer solution containing a photochromic colorant to form a casting film; (2) a method of melt-extruding a thermoplastic polymer containing a photochromic colorant to form a film; (3) a method of preparing and using a composition for forming a film, the composition containing a photochromic colorant; (4) a method of preparing and using an adhesive composition containing a photochromic colorant; (5) a method of thermally diffusing a photochromic colorant in a film or a substrate to form a photochromic diffusion layer; and the like (e.g., Patent Document 1).
One method for applying any of the functional layers described above to optical items such as sunglasses, goggles, corrective lenses and the like uses a functional sheet including protective layers on both surfaces of a layer having polarization properties, a layer having photochromic properties, or a layer having both of these properties.
An example of a transparent plastic material usable for the protective layer is a thermoplastic resin. Examples of the thermoplastic resin include aromatic polycarbonate, polymethylmethacrylate, transparent nylon, acetyl cellulose and the like.
Among these materials, aromatic polycarbonate is used from the viewpoint of impact resistance. Polymethylmethacrylate, transparent nylon, hydrocarbon-based resins having an alicyclic substance as a main chain, acetyl cellulose and the like are used from the viewpoints of crack resistance, fashionability, and various other requirements.
A functional layer and a protective layer are integrated together usually by use of a curable resin adhesive, but troubles sometimes occur due to adhesion failure between the functional layer and the protective layer.
Especially when aromatic polycarbonate is used for the protective layer, such an adhesion failure is often observed as delamination of the aromatic polycarbonate protective layer from the adhesive layer.
Aromatic polycarbonate has a problem of causing solvent cracks. Therefore, depending on the solvent used, an adhesive layer cannot be formed on the layer of aromatic polycarbonate, and moreover, the remaining solvent causes cracks. However, if excessive drying is performed for the purpose of removing the solvent, the adhesive strength is usually weakened. There are also limitations on forming an adhesive layer on both adherend surfaces of aromatic polycarbonate for the purpose of realizing strong adhesion.
In order to alleviate this problem, it is easily conceivable to form a protective layer against the adhesive agent on an adhesive surface of aromatic polycarbonate. In the case where the functional sheet includes a protective layer formed of aromatic polycarbonate, plasma treatment is performed as a preparatory treatment for usual adhesion.
However, there is no document found yet which directly refers to forming a protective layer against the adhesive agent.
For other purposes, for example, for producing a thermosetting lens using a functional sheet, there are methods by which a film resistant against a curable resin monomer solution is formed on a surface of a functional sheet, for example, a film of a curable acrylic-based resin or the like is formed on a surface of a functional sheet (Patent Documents 2 and 3).
An optical item such as sunglasses, goggles, corrective lenses or the like using the above-mentioned functional sheet is usually produced as follows. First, the functional sheet is molded to be a lens which is curved as desired. Alternatively, the functional sheet is molded to be a bent item having a curved surface, then the bent item is attached to a mold, and a rear surface thereof is provided with a transparent plastic material by means of injection molding, thereby forming a lens. The lens obtained by either method is subjected to hard-coating, reflection prevention, and any other surface treatment when desired. Then, the steps of shaping the lens to fit into the frame (external shape processing), drilling holes, and tightening with screws, and the like are conducted. In this manner, the optical item is assembled.
While being handled as described above, the layer of the transparent plastic material is exposed to stresses caused by abrasion, bending, compression, tension, twisting, non-uniform deformation due to temperature or humidity change, and the like. Among these, abrasion on the surface layer of the transparent plastic material is a problem. When the material is not highly resistant against abrasion, a product having scratches is liable to be provided, which lowers the production yield.
Among the above-described functional sheets, a functional sheet including an aromatic polycarbonate layer, which is highly impact resistant, is easily scratched. Therefore, such a functional sheet is, for example, hard-coated after being produced (Patent Document 4).
Patent Document 5 describes that a protective layer formed of a (meth)acrylic-based resin may have an insufficient mechanical strength or the like, and thus a polycarbonate-based resin layer is provided on an outer surface of a (meth)acrylic-based resin forming a protective layer so that the polycarbonate-based resin layer acts as an outer surface of the functional sheet.